1. Field of the Invention
The present invention relates to a performing action related to handover, and more particularly, to a method of performing actions related to handover by a mobile station (MS) that is in power saving mode in a wireless mobile communication system.
2. Discussion of the Related Art
In a broadband wireless access system, a power saving mode or a sleep mode can be used to minimize power consumption of a mobile station (MS). The power saving mode comprises a sleep interval and a listening interval, which are repeated during the operation by the MS. A length (or duration) of the sleep interval is determined by a value of a sleep window. Similarly, a length (or duration) of the listening interval is determined by a value of a listening window. These values are respectively determined based on a characteristic of a determined traffic of a corresponding MS. Furthermore, the MS can be represented by three (3) types of power saving class according to the characteristics of traffic associated with the power saving class.
More specifically, the three power saving class types are classified as a power saving mode class type 1 (hereinafter “Class 1”), a power saving mode class type 2 (hereinafter “Class 2”), and a power saving mode class type 3 (hereinafter “Class 3”).
Class 1 can be defined by an initial sleep window, a final window base, a final window exponent, a listening window, and a start frame number of sleep window. Furthermore, Class 1 focuses on features such as Best Effort (BE) which characterizes the existing interne traffic or non-real-time variable rate (nrt-VR).
Class 2 can be defined by an initial sleep window, a listening window, and a start frame number of sleep window. Furthermore, Class 2 focuses on features such as Voice over Internet Protocol (VoIP) and the nrt-VR.
Class 3 can be defined by a final window base, a final window exponent, and a start frame number of sleep window. Furthermore, Class 3 is for periodically transmitting a management message, such as a Downlink Channel Descriptor/Uplink Channel Descriptor (DCD/UCD) and a neighbor advertisement (MOB_NBR_ADV), to the MS that is in power saving mode or alternatively, for data transmitted via multicast transmission.
The above power saving class types describe different types of power saving modes. The operations of these different class types are the basis for handover for the MS to a base station (BS). While in power saving mode, the MS receives signal quality information of neighbor base stations. The signal qualities of neighbor bases stations can be measured by performing scan operation. Before handover operation is performed, a serving BS transmits handover trigger information, which is used in performing handover, to the MS. Here, the serving BS refers to the BS which granted the MS to enter the power saving mode. Using the received handover trigger information, the MS performs handover when the condition specified in the handover trigger information is satisfied.
Even if the MS that is in power saving mode does not transmit and receive a scan request message and a scan response message, respectively, the MS performs scan operation on neighboring base stations and measures signal qualities of neighbor base stations. If the results of the scan operation (e.g., signal qualities of the neighbor base stations, the received signal strength, and/or transmission delay) are transmitted via scan report message to the serving BS every time the scan operation is performed, the power consumption for uplink transmission by the MS increases. At the same time, if the serving BS fails to receive the scan results from the MS operating in power saving mode, then the handover operation of the MS cannot be controlled properly.